Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 250630
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED DEC 24 2014

.SYNOPSIS...
AN UPPER LEVEL TROUGH WILL CONTINUE TO AFFECT THE AREA TONIGHT WITH
POTENTIAL FOR SHOWERS AND PERIODS OF HEAVY RAIN THROUGH EARLY
THURSDAY. THIS UPPER TROUGH IS EXPECTED TO SLOWLY LIFT NORTHEAST AND
AWAY FROM THE AREA DURING THE NEXT COUPLE OF DAYS...WITH DRIER
CONDITIONS RETURNING DURING THE WEEKEND. MODERATE NORTHERLY WINDS
WILL SHIFT TO A MORE TYPICAL TRADE WIND PATTERN BY LATE SUNDAY AND
INTO EARLY NEXT WEEK.

&&

.DISCUSSION...
LATEST WATER VAPOR AND INFRARED SATELLITE IMAGERY DEPICT A SHARP
UPPER LEVEL TROUGH AND AN ASSOCIATED MID LEVEL LOW LIFTING TO THE NE
OF THE ISLANDS...AND STILL KEEPING POTENTIAL FOR SHOWERS AND
LOCALIZED HEAVY DOWNPOURS TONIGHT. BEST CHANCES OF HEAVY RAIN REMAIN
OVER MAUI COUNTY AND THE BIG ISLAND...FOR WHICH A FLASH FLOOD WATCH
REMAINS IN EFFECT THROUGH THURSDAY EARLY MORNING AS THE BEST POOL OF
MOISTURE ASSOCIATED WITH THE TROUGH LINGERS OVER THE E HALF OF THE
ISLAND CHAIN. BUT LOCALIZED HEAVY DOWNPOURS ARE ALSO POSSIBLE OVER
OAHU AND KAUAI TONIGHT.

MEANWHILE...THE UPPER TROUGH IS KEEPING TIGHT PRESSURE GRADIENTS
OVER THE MID LEVELS AND GENERATING VERY STRONG WINDS OVER THE BIG
ISLAND SUMMITS...WITH POSSIBLE PASSING SNOW SHOWERS AFFECTING THAT
AREA AT TIMES. A BLIZZARD WARNING REMAINS IN EFFECT FOR THE SUMMITS
OF MAUNA LOA AND MAUNA KEA THROUGH EARLY THURSDAY MORNING.

THE GLOBAL MODELS SHOW FAIR AGREEMENT REGARDING A SFC LOW PRESSURE
SYSTEM THAT HAS BEEN ADVERTISED AS FORMING SOMEWHERE JUST N OF THE
ISLANDS BY THIS TIME. SO FAR OBSERVATIONS DO NOT SUGGEST THAT THE
ONSET OF THIS EVENT IS ALREADY HAPPENING. THERE IS A TROUGH-LIKE
FEATURE OVER THE CENTRAL PORTIONS OF THE ISLAND CHAIN GRADUALLY
PUSHING N...FROM WHICH THE SFC LOW COULD BE SPAWNED...COUPLED WITH A
HEALTHIER-LOOKING MID LEVEL LOW. IF THIS SFC LOW EVENTUALLY
FORMS...AS ANTICIPATED...STRONGER SFC NW WINDS WILL LIKELY DEVELOP
ACROSS THE ALOHA STATE. BUT IN THE MEAN TIME...WINDS SHOULD REMAIN
ON THE LIGHTER SIDE AND MAINLY FROM THE N TONIGHT AND INTO THURSDAY.
THIS SCENARIO PRESENTS A HIGH LEVEL OF UNCERTAINTY FOR THE WIND
FORECAST DURING THE NEXT 24 TO 48 HOURS AS THE FORECAST SOLUTION
WILL GREATLY DEPEND ON THE LOCATION AND INTENSITY OF THIS LOW.
THEREFORE...EXPECT SEVERAL UPDATES TO THE SHORT TERM WIND FORECAST
DURING THE NEXT COUPLE OF DAYS.

NEVERTHELESS...MODELS DO AGREE IN LIFTING THE TROUGH AND MID LEVEL
LOW COMPLEX FAR TO THE N OF THE AREA DURING THE UPCOMING WEEKEND
WITH A DRIER AIRMASS ESTABLISHING ALOFT. SFC HIGH PRESSURE SHOULD
ALSO DEVELOP NW OF THE ISLANDS WITH WINDS ONCE AGAIN TURNING MORE
TO THE N...BEFORE FINALLY RETURNING TO A MORE TYPICAL TRADE WIND
FLOW PATTERN EARLY NEXT WEEK AS THE SFC HIGH MIGRATES E.

MODELS DEPICT A COLD FRONT REACHING THE ISLANDS BY THE MIDDLE OF
NEXT WEEK...BRINGING POTENTIAL FOR ANOTHER ROUND OF UNSETTLED
WEATHER ACROSS THE ALOHA STATE.

&&

.AVIATION...
MAINLY QUIET CONDITIONS EXPECTED AT ISLAND TERMINALS TONIGHT. A
TROUGH JUST EAST OF THE BIG ISLAND AND EXTENDING NORTH OF THE STATE
HAS PROVIDED LIGHT NORTH TO WEST FLOW OVER THE STATE. THIS WILL
ALLOW FOR LOCALIZED LAND BREEZES OVERNIGHT. EXPECT WIND SPEEDS TO
INCREASE SLIGHTLY TOMORROW AFTERNOON AS THIS FEATURE DEVELOPS INTO A
LOW.

THE CORE OF THE MID TO UPPER LEVEL LOW THAT AFFECTED THE STATE OVER
THE PAST FEW DAYS IS NOW ABOUT 250 NM NORTH OF PHNL. REPORTS
INDICATE THAT THE MOD TURB ASSOCIATED WITH THIS FEATURE HAVE SHIFTED
EAST OF THE ISLANDS. SOME INSTABILITY REMAINS AROUND THE ISLANDS AND
THE AFTERNOON SOUNDINGS SHOW AN ELEVATED INVERSION SLOPING FROM 14
KFT IN LIHUE TO 20 KFT IN HILO. SOME OF THE SCATTERED SHOWERS
OVERNIGHT WILL LIKELY CARRY MVFR CONDITIONS WITH TOPS REACHING ABOVE
15 KFT.

&&

.MARINE...
A HIGH SURF ADVISORY FOR NORTH FACING SHORES OF THE SMALLER ISLANDS
CONTINUES THROUGH THURSDAY. ANOTHER MODERATE NORTHWEST SWELL IS
EXPECTED TO ARRIVE FRIDAY NIGHT...PEAKING ON SATURDAY BEFORE
DECREASING A LITTLE ON SUNDAY. A REINFORCING NORTHWEST SWELL WILL
ARRIVE ON MONDAY.

THE COMBINED SEAS HEIGHTS ARE HIGH ENOUGH TO WARRANT SMALL CRAFT
ADVISORY FOR MUCH OF THE EXPOSED COASTAL WATERS. CONDITIONS SHOULD
IMPROVE ENOUGH BY THURSDAY EVENING SUCH THAT THE ADVISORY MAY BE
ALLOWED TO EXPIRE.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH 6 AM HST THURSDAY FOR MAUI COUNTY AND THE
BIG ISLAND.

HIGH SURF ADVISORY THROUGH 6 PM HST THURSDAY EVENING FOR NORTH
FACING SHORES OF NIIHAU...KAUAI...OAHU...MOLOKAI AND MAUI.

BLIZZARD WARNING THROUGH 6 AM HST THURSDAY FOR BIG ISLAND SUMMITS.

SMALL CRAFT ADVISORY THROUGH 6 PM HST THURSDAY EVENING FOR ALL
HAWAIIAN WATERS EXCEPT FOR MAUI LEEWARD WATERS...BIG ISLAND LEEWARD
WATERS AND BIG ISLAND SOUTHEAST WATERS.

&&

$$

DISCUSSION/MARINE...REYNES
AVIATION...EATON






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